Is it normal if the relief valve drip?

I have a hot water boiler heating system. The pressure relief valve used to leak a gallon water per hour. I have replaced the valve last week. Now it is much better. But it is still dripping a gallon water every a couple of days. Is it normal? I have checked the water pressure which is about 12 psi and the temp is about 80C. The expansion tank seems ok as well.